1. Field of the Invention
This invention relates generally to magnetic recording heads, particularly to perpendicular recording heads that produce recording magnetic fields that are largely perpendicular to the recording medium surface. More specifically, the invention relates to a magnetic pole of a recording head having a tapered shape that allows a more efficient delivery of a magnetic recording field to a recording medium while minimizing the effects of adjacent track erasure (ATE) and wide area track erasure (WATE).
2. Description of the Related Art
The increasing need for high recording area densities (>100 Gb/in2) is making the perpendicular magnetic recording head (PMR head) a replacement of choice for the longitudinal magnetic recording head (LMR head).
By means of fringing magnetic fields that extend between two emerging pole pieces, longitudinal recording heads form small magnetic domains with the magnetic moment in each domain pointing within the surface plane of the magnetic medium (hard disk). As recorded area densities increase, these domains must correspondingly decrease in size, eventually permitting thermal effects to destabilize the small magnetic domains. This occurrence is the so-called superparamagnetic limit.
Recording media that utilize perpendicular magnetic recording, allow domain structures within a magnetic layer to be formed with the net magnetic moment in each domain having a perpendicular orientation relative to the disk surface, while a soft magnetic underlayer (SUL) formed beneath the magnetic recording layer serves to channel a return flux back to the head to strengthen the recording field during the writing process. Thus, a magnetic recording head that produces a field capable of forming domains perpendicular to a disk surface, when used in conjunction with such perpendicular recording media, is able to produce more stable domain configurations with much higher area densities than is possible using standard longitudinal recording.
Although the magnetic media used in conjunction with perpendicular writing are capable of storing a high area density, the write head itself must be able to produce magnetic fields of sufficient intensity and definition to make use of the media's capabilities. One approach to matching the writer capabilities to those of the media is to fabricate a magnetic pole tip that tapers in thickness towards the ABS end (the end adjacent to the recording medium). Such a design makes the pole thicker away from the ABS but presents a smaller footprint where it emerges at the ABS, yet it delivers more flux. U.S. Pat. No. 7,322,095 and U.S. Patent Applications 2008/0112082 and 2005/0237665 (Guan et al.) show such a main pole tapered preferably at its trailing edge and shielded on four sides.
FIG. 1 shows a highly schematic diagram of a side cross-sectional view of a prior art PMR single pole writer positioned above a moving magnetic media (16) such as a magnetic disk. Although the disk is rotating about a central axis, in this part of the figure it is moving locally relative to the main pole of the writer in the direction of the arrow (180). The “leading edge” (indicated in the figure by the legend “Leading Edge”) of the main pole denotes the edge or surface towards which the disk is moving. The opposite surface of the pole is its trailing edge. Typically, a read head, which is not shown here, would be formed to the leading edge side of the writer, so an area on the disk moves past the read head before passing beneath the writer. For consistency of description, a set of orthogonal x, y, z axes define directions in this and remaining figures that display a PMR writer or describe its performance. The positive x-direction points in the direction of disk motion, the positive y-direction points to the rear of the writer, which is away from the ABS surface, the z-direction points towards adjacent tracks in the plane of the disk.
The main pole of the writer (14) is in physical and magnetic contact with a portion of a yoke (18) which in this case is attached (eg. by plating) on “top” of the pole (on its trailing edge) and is, therefore, called a top yoke. Magnetic flux is emitted from the pole tip (19) at its air bearing surface (ABS) at which region it “writes” on the disk by aligning the magnetic moments in the nearby magnetic grains within the disk surface. The flux that exits from the pole tip at (19) passes through the medium and the SUL and returns to the return portion of the yoke (15) to complete a flux loop. The magnetic flux is created by a magnetic field induced by a current in the coil windings (12) wrapped around the pole. One exemplary coil of such coil windings (12) is shown.
Referring now to FIG. 2, there is shown a prior art approach to shaping a main pole so that the flux leaving the ABS surface (19) is more narrowly confined and is able to write with higher definition on smaller regions of the disk surface. The main pole (14) is shown here as being attached to a top yoke (18), as in FIG. 1 (although the view is reversed).
In this design, the ABS tip of the main pole is tapered (narrowed) towards the ABS surface which forms the distal end of the pole. The taper is produced by beveling the tip of the main pole at both its trailing edge (192) and its leading edge (191), although it is possible to have only one of the edges tapered. When the taper terminates, the pole retains a constant thickness until its proximal end, which, as the terms “proximal” and “distal” will be used herein, is the end farthest from the (distal) ABS, end.
The methods by which the pole tip is tapered and the general design of the taper are also taught in the following patents and published applications.
U.S. Patent Application 2005/0219743 (Guan et al—Headway) discloses that the main pole may be tapered at the leading or the trailing edge.
U.S. Pat. No. 7,133,252 (Takano et al) shows that the main pole may be tapered at the leading edge or the trailing edge or both.
U.S. Pat. No. 5,600,519 (Heim et al) discloses a tapered pole tip.
U.S. Patent Application 2008/0316653 (Sasaki et al). FIG. 12 shows the pole tapered and the nonmagnetic layer 17 also tapered.
Although the various tapered pole configurations described above have advantages when compared to pole tips that are not tapered, such as improved field strength, they also possess certain shortcomings. In particular, the thicker region of the pole tip (the region proximal to the ABS taper) causes increased flux to be channeled into the surrounding region around the main pole, in addition to some enhancement of flux density within the main pole, causing significant fringing of the emerging magnetic field when it emerges at the pole tip. This fringing, which can be exacerbated by shield configurations, leads to track erasures on adjacent tracks (ATE) as well as on tracks within a wider area (WATE). In addition, the length of the thicker region of the pole (proximal to the taper) will contain a large amount of flux, a small part of which is then concentrated within the tapered region to produce the improvement in writing flux intensity along with significant fringing. This implies that there is a great deal of magnetic flux circulating within the head in order to produce the required concentrated flux at the tip. It would be desirable to create a pole tip design that provides the necessary enhancement for writing within very small areas, while minimizing ATE and WATE and also reducing the net amount of flux circulating within the head.